The design and implementation of bionic organs and devices that enhance human capabilities, known as cybernetics, has been an area of increasing scientific interest. This field has the potential to generate customized replacement parts for the human body, or even create organs containing capabilities beyond what human biology ordinarily provides. In particular, the development of approaches for the direct multidimensional integration of functional electronic components with biological tissue and organs could have tremendous impact in regenerative medicine, prosthetics, and human-machine interfaces. Recently, several reports have described the coupling of electronics and tissues using flexible and/or stretchable planar devices and sensors that conform to tissue surfaces, enabling applications such as biochemical sensing and probing of electrical activities on surfaces of the heart, lungs, brain, skin, and teeth. However, attaining seamless three dimensionally (3D) entwined electronic components with biological tissues and organs is significantly more challenging. Tissue engineering is guided by the principle that a variety of cell types can be coaxed into synthesizing new tissue if they are seeded onto an appropriate three-dimensional hydrogel scaffold within an accordant growth environment. Following in vivo or in vitro culture, tissue structures form which possess the morphology of the original scaffold. A major challenge in traditional tissue engineering approaches is the generation of cell-seeded implants with structures that mimic native tissue, both in anatomic geometries and intratissue cellular distributions. Techniques such as seeding cells into nonadhesive molds or self-folding scaffolds have been used to fabricate three-dimensional tissue constructs with complex 3D geometries. Yet, existing techniques are still incapable of easily creating organ or tissue parts with the required spatial heterogeneities and accurate anatomical geometries to meet the shortage of donor organs for transplantation. For instance, total external ear reconstruction with autogenous cartilage with the goal of recreating an ear that is similar in appearance to the contralateral auricle remains one of the most difficult problems in the field of plastic and reconstructive surgery.
Additive manufacturing techniques such as 3D printing offer a potential solution via the ability to rapidly create computer-aided design (CAD) models by slicing them into layers and building the layers upward using biological cells as inks in the precise anatomic geometries of human organs. Variations of 3D printing have been used as methods of solid freeform fabrication, although its use has mainly been limited to the creation of passive mechanical parts. Extrusion-based 3D printing has been used to engineer hard tissue scaffolds such as knee menisci and intervertebral discs complete with encapsulated cells. This technique offers the ability to create spatially heterogeneous multi-material structures by utilizing deposition tools that can extrude a wide range of materials. Further, nanoscale functional building blocks enable versatile bottom-up assembly of macroscale components possessing tunable functionalities. This could allow for the simultaneous printing of nanoelectronic materials and biological cells to yield three dimensionally integrated cyborg tissues and organs exhibiting unique capabilities.